It is well known in the art to provide removable shielding adapted to engage a hypodermic syringe in such manner as to surround the barrel thereof and thereby shield a user from radiation emanating from the radioactive contents of the syringe. Most such devices include a bayonet-type locking means at the upper end thereof adapted to engage the outwardly projecting syringe flanges formed integrally with the barrel and normally contacted by the fingers of the user during the discharge of the syringe. Prior art syringe shields also include a single shield barrel formed of lead which covers the major portion of the length of the syringe barrel, leaving an exposed lower syringe end to permit determination of whether or not the syringe is loaded.
There are several disadvantages in the use of this construction. One is the substantial weight of the lead shielding, often heavier than the weight of the syringe itself, and tending to make manipulation of the syringe awkward. Another is the fact that the exposed lower end of the syringe is the point of greatest radiation, and it is normally exposed at all times. Further, in order to calibrate the radiopharmaceutical dose in the syringe, it is usually necessary to remove the syringe from engagement within the shield, and during this process, the user is fully exposed to radiation. While such radiation is normally not dangerous to a patient, it is to be appreciated that the technician using the syringe is exposed to similar radiation on a daily basis, the total accumulation of such radiation being inherently dangerous. The term dose calibration is intended to mean, in this specification, the placing of a loaded syringe in the proximity of radiation measuring means, rather than the loading of the syringe to a predetermined volume. This dose calibration is preferably accomplished immediately before use, since the radioactive materials normally injected decay very rapidly, and often lose all effective strength over the course of several days.
There has recently been developed by the National Institutes of Health, Bethesda, Md., an improved shield made in two parts, including an upper shield element arranged in telescopic fashion with respect to a lower shield element, the upper shield element being of lightweight metal, the lower being of very dense metal such as tantalum or tungsten. This structure permits the confining of shielding material in the area where radiation is greatest, namely at the lower end of the barrel, and the retraction of the lower shield for dose calibration without the necessity of completely removing the shield from the syringe. As might be expected, the cost of manufacture of such devices results in a very high unit cost, making desirable the ability to use the shield with syringes of different manufacture, having different barrel lengths, graduation orientation, diameters, and flange geometry which may vary substantially in comparable syringes of the same capacity. It is further desirable that means be provided for maintaining the sliding relation between the upper and lower shield elements in fixed adjustment to accommodate the aforementioned corresponding differences in syringe construction.